Bulgaria and RCD

[Jimj40]

Hi, All - and greetings from a newbie in Bulgaria!

I wasn't sure if this should go in the DIY section or here, since both are relevant, so apologies if I made the wrong choice.

In a nutshell, our house in Sofia is "old", ie 1990(!) and very substantial. There is a supply coming in which is earthed but, as is often the case here, the circuits themselves aren't earthed as such but what would be the earth is actually tied to the neutral. Just to make things more "interesting" all the cables, even new ones, are just plastered into the walls.

We have some stainless steel outside lights, which are welded onto a ss balustrade around the garden. Obviously, I wanted to get some sort of RCD protection at least for the outside lights but our local well-qualified electrician said there was no point since there was no real earth in the circuit. I have to assume that he is correct but I'm none too crazy about lights outside without any means of guarding against grabbing a metal balustrade and becoming the new earth conduit myself....

So, any thoughts about how I might be able to build in better protection without gutting the whole house would be gratefully received!

 

[davesparks]

I agree, but in this case the ground to neutral bond must be removed at the sockets protected in order for the RCD to function without sporadic tripping.







I agree that a PEN should never be broken, but useing TN-C all the way to a socket passed the main incomer is a very bad idea. He will need to remove the jumper and convert the PEN to a neutral. Even if his RCD never broke the PEN it will always trip. You can not use an RCD on a TN-C system even if it does not break the PEN.

So you are now suggesting removing the earth from the entire installation? That is far worse than maintaining the TNC installation.

Converting the PEN conductor to purely a neutral without also installing a cpc to every point is by far more dangerous than maintaining it as it is

 

[Gardner]

So you are now suggesting removing the earth from the entire installation? That is far worse than maintaining the TNC installation.

Converting the PEN conductor to purely a neutral without also installing a cpc to every point is by far more dangerous than maintaining it as it is

I am suggesting the neutral to earth jumper be removed from the entire installation if an RCD is to work.

I disagree that is dangerous. Both are not the best, but having an RCD and no earth is far safer than having a PEN.

What if the PEN broke? Everything will now be 220 volts to earth. How is that less dangerous than an RCD?

 

[davesparks]

I am suggesting the neutral to earth jumper be removed from the entire installation if an RCD is to work.

I disagree that is dangerous. Both are not the best, but having an RCD and no earth is far safer than having a PEN.

What if the PEN broke? Everything will now be 220 volts to earth. How is that less dangerous than an RCD?

I would much rather have an earth connected at every point (even if it is in the form of a combined neutral and earth) than rely on an RCD!

RCDs have been proven time and again to be unreliable.

Under uk regulations it is not permitted to have an RCD as the sole means of fault protection, you can only use it in addition to ADS.

 

[Gardner]

I would much rather have an earth connected at every point (even if it is in the form of a combined neutral and earth) than rely on an RCD!

An RCD is far less likely to fail than a splice/joint/connection. A branch circuit has many, many connections that can fail for a variety of reasons. All it takes is one connection to fail, and everything will be energized 220 volts to earth after the break which can easily kill a person.

RCDs have been proven time and again to be unreliable.

Yes they do fail, but my understanding is the British RCDs are nothing more than a toroid coil and a solenoid. A connection is far more likely to fail.

If a fault did develop in an appliance on an RCD system any current leakage over 30 milli amps would trip it. 30ma is unlikely to kill an adult.

A broken PEN however will allow far more than 30ma to flow through a persons body, which is lethal.

Under uk regulations it is not permitted to have an RCD as the sole means of fault protection, you can only use it in addition to ADS.

You may have a point. But is that only new installations? What about old ones where you just have 2 wires and a non grounding socket. Do you just install an earthing socket and jumper neutral to earth at the socket?

 

[shanky887614]

? i dont follow surely you would have them linked before the board then seperate from a henley (same as from dno in tncs) then it shouldn't trip the rcd in the board

 

[davesparks]

An RCD is far less likely to fail than a splice/joint/connection. A branch circuit has many, many connections that can fail for a variety of reasons. All it takes is one connection to fail, and everything will be energized 220 volts to earth after the break which can easily kill a person.





Yes they do fail, but my understanding is the British RCDs are nothing more than a toroid coil and a solenoid. A connection is far more likely to fail.

If a fault did develop in an appliance on an RCD system any current leakage over 30 milli amps would trip it. 30ma is unlikely to kill an adult.

A broken PEN however will allow far more than 30ma to flow through a persons body, which is lethal.






You may have a point. But is that only new installations? What about old ones where you just have 2 wires and a non grounding socket. Do you just install an earthing socket and jumper neutral to earth at the socket?

Branch circuit? What's that when it's at home?

Studies have been carried out where it has been proved that unless the test button is pushed regularly then the mechanisms seize and prevent the RCD from operating.
Plus RCDs just fail for no reason sometimes.

A broken PEN will be the same as a broken CPC in that respect but we don't install RCDs on every circuit to protect against this! We install circuits properly and test them in accordance with the regulations, recording test results and referencing them to previous tests to identify any deterioration.

What do you mean by a non-grounding socket? Do you mean something like a socket with no earth? The only time you see such a thing in general use in the uk is supplied from an isolating transformer.

These days you wouldn't install any new wiring on to an existing TNC installation (if you can even find one) only carry out repairs of necessary

 

[davesparks]

? i dont follow surely you would have them linked before the board then seperate from a henley (same as from dno in tns) then it shouldn't trip the rcd in the board

The installation is supplied from a TNC service and uses a single conductor for both N and cpc throughout the installation.

 

[shanky887614]

The installation is supplied from a TNC service and uses a single conductor for both N and cpc throughout the installation.

converting toto a tncs before the board would be safer than no earth

 

[Gardner]

Branch circuit? What's that when it's at home?

Any circuit after the electrical panel. Be it for lights, sockets, appliances.

Studies have been carried out where it has been proved that unless the test button is pushed regularly then the mechanisms seize and prevent the RCD from operating.
Plus RCDs just fail for no reason sometimes.

I am not disputing RCDs fail, but circuit connections fail a lot more. And considering this is an older installation probably made while Bulgaria was still under communist control I highly doubt is reliable. A new ABB or Hager RCD would be a lot more dependable.

A broken PEN will be the same as a broken CPC in that respect but we don't install RCDs on every circuit to protect against this! We install circuits properly and test them in accordance with the regulations, recording test results and referencing them to previous tests to identify any deterioration.

CPC? Sorry. If you mean Earth wire, not the case. A broken earth wire will not energize everything. And an earth wire is far less likelly to fail at a connection since it does not normally carry current. And in any case should an earth break and a fult occur an RCD is the last line of defense against electrocution.

I know that new circuits require an earth, but existing installations with no earth?

What do you mean by a non-grounding socket? Do you mean something like a socket with no earth? The only time you see such a thing in general use in the uk is supplied from an isolating transformer.

A socket without an earth pin. Have these ever been used in the UK? Perhaps not, but were very common in the 1950s all over the world, especially the US.

These days you wouldn't install any new wiring on to an existing TNC installation (if you can even find one) only carry out repairs of necessary

Thats the thing, TN-C all the way up to the socket has never been allowed in most countries.

 

[ImpededLoop]

So would you be comfortable with an RCBO which only breaks the line conductor when it operates?

 

[davesparks]

converting toto a tncs before the board would be safer than no earth

How would you suggest doing that? There are only 2 cables for each circuit 1xlive and 1xPEN (protective earthed neutral) this is covered in bs7671 as the method was acceptable for installations before the 14th edition

It does have an earth at the moment, it is combined with the neutral in one wire.

 

[davesparks]

Branch circuit? What's that when it's at home?

Any circuit after the electrical panel. Be it for lights, sockets, appliances.






I am not disputing RCDs fail, but circuit connections fail a lot more. And considering this is an older installation probably made while Bulgaria was still under communist control I highly doubt is reliable. A new ABB or Hager RCD would be a lot more dependable.





CPC? Sorry. If you mean Earth wire, not the case. A broken earth wire will not energize everything. And an earth wire is far less likelly to fail at a connection since it does not normally carry current. And in any case should an earth break and a fult occur an RCD is the last line of defense against electrocution.

I know that new circuits require an earth, but existing installations with no earth?





A socket without an earth pin. Have these ever been used in the UK? Perhaps not, but were very common in the 1950s all over the world, especially the US.







Thats the thing, TN-C all the way up to the socket has never been allowed in most countries.

TNC was allowed on installations prior to the 14th edition of the regulations being introduced.
I've got an old bicc reference book somewhere which describes the use of single core micc for this type of installation

 

[Gardner]

So would you be comfortable with an RCBO which only breaks the line conductor when it operates?

Yes, but an RCD measures differences in current. In a PEN current always divides between it and any other earthed object its connected to. In this installation nuisance tripping will happen constantly.

 

[ImpededLoop]

Yes, but an RCD measures differences in current. In a PEN current always divides between it and any other earthed object its connected to. In this installation nuisance tripping will happen constantly.

That's a good point. It's obvious when you think about it! [emoji3]

 

[Gardner]

Branch circuit? What's that when it's at home?

TNC was allowed on installations prior to the 14th edition of the regulations being introduced.
I've got an old bicc reference book somewhere which describes the use of single core micc for this type of installation

And that may have been the case, but is still dangerous. In the US TN-C was never allowed for general sockets or circuits. Up until the 1960s we had 2 wire none earthing sockets, however when installing new 3 wire sockets on those circuits we must install an RCD. We CAN NOT jumper the neutral to ground. If we did any electrician could loose their license. It is well known that a neutral can never be guaranteed to function as a grounding conductor passed the service.


Here is how we install 3 wire sockets on old 2 wire circuits:

http://ecmweb.com/site-files/ecmweb.com/files/archive/ecmweb.com/mag/410ecm17fig2.jpg

http://ecmweb.com/site-files/ecmweb.com/files/archive/ecmweb.com/images/201ecmCQfig1.gif

DIY vid, but very detailed and explains the correct way to do it:

https://www.youtube.com/watch?v=twhzCgVst80










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